The present invention generally relates to video signal slow-motion or still picture reproduction systems, and more particularly to a system capable of performing slow-motion reproduction or still picture reproduction so that noise is not introduced in the reproduced picture.
Systems have been known wherein a video signal is recorded on a magnetic tape on parallel tracks formed obliquely with respect to the longitudinal direction of a magnetic tape. The magnetic tape travels at a speed which is different from that at the time of recording or stops, for carrying out speed-change reproduction such as quick-motion reproduction, slow-motion reproduction, or still picture reproduction. In such a system, because the tape speed upon speed-change reproduction is different from that at the time of recording, the path (track) over which a head traces over the tape during this speed-change reproduction is different from the path (track) on the tape traced by the head upon recording.
The conventional video signal recording and reproducing system ordinarily forms tracks on a recording medium in a manner which leaves an unrecorded zone or band called a guard band between adjacent tracks. This is in order to prevent beats from being generated when the head reproduces adjacent tracks due to tracking error upon normal reproduction. When the tape recorded in this manner is played back by speed-change reproduction as described above, the head traces over the track and the unrecorded band. When the head traces over the unrecorded band, the level of the reproduced signal becomes considerably low or becomes zero. For this reason, noise is introduced in the reproduced picture. Further, since the unrecorded bands are provided between the tracks in the above described system, the utilization efficiency of the tape was poor.
Accordingly, a system has been previously proposed wherein tracks are formed on the tape without gaps formed between the adjacent tracks, and moreover, a color video signal can be recorded and reproduced without introducing beat disturbance. Such a system is disclosed in the U.S. Pat. No. 4,178,606 entitled "COLOR VIDEO SIGNAL RECORDING AND/OR REPRODUCING SYSTEM" issued on Dec. 11, 1979 and assigned to the same assignee as that of the present application. In this previously proposed system, a pair of heads having gaps of mutually opposite azimuth angles with respect to a direction perpendicular to the longitudinal direction of the track are used, and the adjacent tracks are formed in contiguous contact side-by-side without a gap formed therebetween. The phase of the chrominance signal is shifted by 90.degree. for every horizontal scanning period. Moreover, the direction of this phase shift is reversed for every adjacent track. According to this system, the tape utilization efficiency is high since the tracks are in close contact with each other. In addition, the beat disturbance is not introduced.
Then, another system was proposed which uses the above proposed system. In this system, a plurality of rotary heads having gaps with centers along the track width direction which are different in height positions with respect to the rotational planes in which the heads travel, are used. The magnetic tape travels at a speed V which satisfies the following equation, where Vo is the tape speed for normal reproduction (and recording), and n is a positive or negative integer. ##EQU1## Hence, the tape may be stopped or caused to travel so as to carry out still picture reproduction or slow-motion reproduction.
This latter proposed system is capable of carrying out slow-motion reproduction or still picture reproduction with reduced noise. However, the magnetic tape must travel at a speed satisfying the above equation. This gives rise to a problem in that slow-motion reproduction cannot be carried out at arbitrary speeds. Moreover, when the traveling magnetic tape is to be stopped for still picture reproduction, the position where the magnetic tape stops is not controlled. Accordingly, the operator must search for a position to stop the magnetic tape where the noise is minimum, while monitoring the reproduced picture screen. Thus, there is a disadvantage in that the operation is quite troublesome to perform.
Accordingly, in the U.S. Pat. No. 4,246,616 in which the assignee is the same as that of the present application, a system was proposed for reproducing a video signal in a slow-motion or still picture reproduction mode, in order to overcome the above described problems.
In this third proposed system for reproducing a video signal in a slow-motion or still picture reproduction mode, the video signals are recorded along video tracks on the tape. The video tracks extend obliquely with respect to the longitudinal direction of the tape, with substantially no gap formed therebetween. A control signal is recorded along a control track extending in the longitudinal direction of the tape, and the video tracks are recorded by a plurality of rotary video heads having gaps of mutually different azimuth angles. The control signal is recorded along the control track interrelatedly with the recording of the video tracks by the video heads. A motor drives the tape to travel or stop. The plurality of rotary video heads successively trace over the video tracks to pick up and reproduce the recorded video signals. The gaps of the rotary video heads have different height positions above the plane of rotation of the centers of the tracks in the width direction of the track. The control signals are reproduced from the control track of the traveling tape. A circuit delays the reproduced control signal by a predetermined delay time, to obtain a delayed signal, and uses this delayed signal to stop the motor and the tape trave. The tape is stopped at a position relative to the video heads which perform reproduction, so that the time instant when the level of the reproduced video signal becomes a minimum is within or in the vicinity of the vertical blanking period.
According to this third proposed system, still picture reproduction during the above slow-motion reproduction is carried out in a state without generating noise, and thus, the slow-motion reproduction as a whole is carried out without generating noise. By selecting the above described still picture reproduction at will, slow-motion reproduction can be carried out with an arbitrary slow-motion ratio. In addition, still picture reproduction can be carried out by continuing the above still picture reproduction period.
When performing the above slow-motion reproduction or the still picture reproduction, it is necessary to stop the magnetic tape at a most suitable position with respect to the rotary video heads by tape travel stopping means. Conventionally, as this tape travel stopping means, there was means for immediately stopping the rotation of a capstan motor by short-citcuiting the terminals thereof, means for stopping the tape travel by using the inertia of the capstan and a flywheel and taking into account the magnitude of the braking with respect to the capstan motor, and means provided with a second control head for immediately stopping the rotation of the capstan motor when this second control head reproduces a control pulse.
However, in the above conventional tape travel stopping means, although the reproduced control signal is used as a reference signal for stopping the tape travel, there is no feedback to determine whether the noise is actually within the vertical blanking period and does not appear in the reproduced picture. Thus, after the control pulse is detected, discrimination could not be performed to determine whether the magnetic tape is actually stopped at the most suitable stopping position. Accordingly, in the conventional reproducing system, if the various conditions with respect to the mechanisms in the VTR change, it became necessary to re-adjust the tracking every time such change is introduced.